In particular soils (incoherent sands or silts, peat layers, plastic clays etc.), it is difficult to transfer compression and/or tension loads; it becomes therefore necessary to intervene with technical solutions, for instance using alternative expensive systems of foundation (jet grouting, tubfix micropiles, etc.).
These systems have the tendency to create in one or more points of the pile, of the tie rod and of the foundation wall or of the masonry chain, some bulbs that improve the possibility to transfer loads from the superstructure to the soil or to another structure or alternatively to oppose to the loads themselves.
Another way consists of assigning to the structure of foundation minimum bearing capacity because of the soil's very low strength parameters.
In some cases it is necessary to perform repeated injections of cement mixing to improve the soil characteristics, with very expensive costs.
In the case of tie rods—with harmonic steel reinforcement section, or steel bars with elevated tensile limit to anchor to the ground, for instance, walls of support, radio antennas, etc.—it can happen that the performance is not successful due to the poor mechanical characteristics of the soil, incapable to resist to tensile forces. Consequently necessary reconstruction works are requested or, alternatively, new tie rods with lower tensile capabilities.
The same can be said for foundation piles, where low strength parameters compel the design engineer to reduce the unit load by increasing the total number of pile for the overall foundation.
Another problem is related to the execution of the works of improvement of the soil, that requires full skill and ability of the operator strictly coming from his experience, the perfect functionality of the operative equipments and homogeneity of the soil complex; all these things are not always verifiable.